Rotating blowout preventers are known to those skilled in the drilling art, and are usually referred to as RBOPs; or, rotary stripper devices. There is hardly ever a borehole of any significance sunk into the ground without the employment of at least one high pressure rotary stripper device. The RBOP enables a driving member, such as a drill string, or the kelly of a drill string, to be slidably forced axially therethrough. The RBOP includes a stripper rubber assembly rotatably mounted respective to a main body so that the driving member and stripper rubber assembly rotate in low friction relationship respective to the remainder of the RBOP, and at the same time the drill string can be slidably positioned axially respective to the RBOP.
The stripper rubber assembly of the RBOP enables various different sizes of tubular goods to be forced downhole and retrieved from the high pressure interior of the borehole. However, from time to time, a larger or smaller elongated member must be connected within the drill string and placed within the borehole; and, for this reason it is advantageous to be able to readily remove the stripper rubber assembly from the main housing of from the RBOP so that a different size stripper rubber assembly can be employed therewith. Alternatively, in some instances, it is possible for the stripper rubber assembly to be removed from the main body, the elongated member passed downhole, or retrieved from the borehole, whereupon the stripper rubber assembly is again positioned within the main housing of the RBOP and the operation resumed.
RBOPs are usually quite complex, and may include more than a hundred parts. Therefore, the cost of the RBOP usually is directly proportional to its complexity. The RBOP is complex in design because it must be fabricated in such a manner to adequately resist the heavy forces resulting from upthrust and downthrust of the stripper rubber assembly, as well as the lateral forces imposed on the stripper rubber assembly.
In the past, accommodation of the above mentioned forces has been achieved by employing various different large and expensive ball bearings and tapered roller bearings which must be provided with an inside diameter of a size to accommodate the required stripper rubber assembly. The massive bearings require extensive design techniques in order to maintain them in proper operative condition, and in order to achieve a reasonable operational life expectancy. Needless to say, bearings of the required size and design are quite expensive.
My previous patents, U.S. Pat. Nos. 4,154,448 and 3,868,832, and U.S. Pat. No. 3,725,862, disclose an RBOP which can be advantageously employed as a high pressure rotary stripper.
The Murray patent, U.S. Pat. No. 4,157,186 and the Bunting, et al patent, U.S. Pat. No. 4,143,880, disclose an RBOP which can also be used in drilling some boreholes. The above mentioned RBOPs have performed satisfactorily during most drilling operations, however, the cost thereof is appreciable, and for this reason it would be desirable to have made available a reliable RBOP having a minimum number of parts, which is dependable in operation and which is uncomplicated in design. Such an RBOP is the subject of the present invention.